Crimson Court (CC) is decent DLC. However, like the base game, it suffers from the same issues. It has interesting concepts, good artwork, great narration, but poor gameplay mechanics. I think some of the worst issues have been ironed out with patches. But it is still a grindy, tedious experience, unnecessarily drawn out by a questionable disease system and overly long dungeons that have you searching for keys and running into dead ends (you'll need to look up some maps on the internet to figure out the 3 main dungeons).
Still, all is not lost. There are mods that can make CC worthwhile. For a game (Darkest Dungeon) that has more than its share of diseases and afflictions already, you can mod CC to tone down the new disease or disable it all together (which is what I did). The new bosses are tough and well done, though you'll have to endure the ridiculously long dungeons to find them. CC adds more trinkets and district buildings, which are helpful in the base game as well. Once you finish the last boss fight, there is really nothing else to do. However, for $10, it's worth it, especially with mods.